Packaging and storage— Preserve in well-closed containers.

USP Reference standards á11ñ— USP Polymyxin B Sulfate RS.USP Bacitracin Zinc RS.

Microbial limits— Collect aseptically in a suitable container about 1g from not less than 5containers,dissolve in 500mLof Fluid A,filter through a membrane filter as directed for Membrane Filtrationunder Test for Sterility of the Product to be Examinedunder Sterility Tests á71ñ,except to place the filter on the surface of Soybean–Casein Digest Agar Medium in a Petri dish,incubate for 7days at 30to 35,and count the number of colonies on the filter.Similarly prepare a second specimen,except to incubate at 20to 25.Not more than 20colonies are observed from the two specimens.It meets also the requirements of the tests for absence of Staphylococcus aureusand Pseudomonas aeruginosaunder Microbial Limit Tests á61ñ.

Water,Method Iá921ñ: not more than 7.0%.

Assay for polymyxin B— Proceed as directed for polymyxin Bunder Antibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Topical Powder,equivalent to about 5000USP Polymyxin B Units,shaken with 20mLof water in a suitable volumetric flask.Dilute with Buffer No.6to volume,and mix.Dilute an accurately measured volume of the solution so obtained quantitatively with Buffer No.6to obtain a Test Dilutionhaving a concentration of polymyxin Bassumed to be equal to the median dose level of the Standard.

Assay for bacitracin— Proceed as directed for bacitracin under Antibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Topical Powder,equivalent to about 800USP Bacitracin Units,added to a 100-mLvolumetric flask,dilute with 0.01Nhydrochloric acid to volume,and mix.Dilute this solution quantitatively with Buffer No.1to obtain a Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard.In preparing each test dilution of the Standard,add additional hydrochloric acid to each to obtain the same concentration of hydrochloric acid as in the Test Dilution.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 1578

Phone Number:1-301-816-8335